Methods useful for affixing a metal tube, namely a tube having a lumen surrounded by a metal wall, to a metal body having a passageway, especially also in connection with the manufacture of measuring transducers of the vibration-type, are described in, among others, German patent, DE-A 102006011789, and U.S. Pat. Nos., US-A 2003/0084559, US-A 2005/0172731, US-A 2006/0083941, US-A 2007/0277624, US-A 2008/0124186, U.S. Pat. Nos. 5,610,342 or 6,047,457, not least of all also methods, in the case of which, first of all, a portion of the respective metal tube is placed in the passageway of the respective metal body, in such a manner that an outer surface of the metal tube and an inner surface of the passageway at least partially contact one another, and thereafter, by deformation of the respective metal body in such a manner that this durably introduces radial forces into the metal tube, a force-based interlocking affixing the metal tube to the metal body, respectively a composite system composed of metal body and metal tube, is formed. The principle construction as well as the principle operation, as well as also options of application of such measuring transducers of the vibration-type formed by means of at least one metal tube useful as measuring tube are known, per se, to those skilled in the art, not least of all also from the above cited German patent, DE-A 102006011789, and U.S. Pat. Nos., US-A 2003/0084559, US-A 2005/0172731, US-A 2006/0083941, US-A 2007/0277624, US-A 2008/0124186, U.S Pat. No. 5,610,342, respectively U.S. Pat. No. 6,047,457, however, among others, also from US- 2011/0146416, US-A 2007/0151370, US-A 2007/0186685, US-A 2008/0127719, US-A 2010/0251830, US-A 2011/0265580, U.S. Pat. Nos. 5,796,011, or 6,006,609. As is known, the at least one metal tube serviceable as measuring tube in the case of such measuring transducers is, especially, adapted to guide in its lumen a fluid, for example, a gas, a liquid or a flowable dispersion, flowing at least at times, especially namely to be flowed through by the fluid and during that to be so caused to vibrate that the metal tube executes mechanical oscillations about a static resting position thereof, mechanical oscillations which are suitable to induce in the flowing fluid Coriolis forces dependent on a mass flow rate and/or frictional forces dependent on a viscosity and/or inertial forces dependent on a density, in order to ascertain, derived therefrom, measured values for the mass flow rate, the viscosity and the density, respectively.
For producing holding forces required for a force-based interlocking in a composite system of the previously indicated type in the case of a press method disclosed in U.S. Pat. No. 6,047,457, respectively US-A 2006/0083941, the respective metal body is cold formed by exerting over an outer surface of the metal body radially inwardly directed deformation forces on the metal body, in such case namely by means of a press machine acting on the metal body via press forms placed on the lateral surface of the metal body. The deformation forces are, in such case, so dimensioned that, as a result of the cold deformation of the metal body, the metal body as well as the metal tube experience, supplementally, elastic deformations, which, as a whole, suffice to establish holding forces between the inner surface of the passageway and the outer surface of the metal tube contacting such for preventing an undesired release of the force interlocking. In the case of another method shown, among others, in US-A 2003/0084559, respectively US-A 2006/0083941, for affixing the metal tube in the metal body, the metal body is for the purpose of forming a force locking with the respective measuring tube thermally shrunk thereon, in given cases, with interpositioning of a metal jacket applied on the metal tube. Furthermore, holding forces required for a force-based interlocking can also be produced by introducing a plastic deformation of the metal tube, in such a manner that the metal tube is widened by deformation forces acting radially outwardly on its inner surface. The widening of the metal tube can, in turn, occur by cold deformation, for example, such as, among others, also disclosed in German patent, DE-A 102006011789, hydraulically, namely by means of a pressurizing medium introduced into the lumen, or, however, for example, also, such as described in U.S. Pat No. 5,610,342, US-A 2006/0083941, respectively US-A 2005/0172731, by an internal rolling method. Used in the case of such an internal rolling method is a roll tool introduced into the lumen of the metal tube, which for effecting a partial plastic deformation of the wall is held pressed against the inner surface of the wall and during that guided along a roll track, for example, a circular, respectively screw thread shaped, roll track, extending within a predetermined deformation region of the metal tube, for example, namely over the total portion of the metal tube accommodated by the passageway of the metal body.
An advantage of such a force-based interlocking is, among other things, that therewith also a metal tube can be affixed to such a metal body, which is composed of a material, which cannot be connected with the material of the wall of the metal tube by material bonding, namely neither welded, nor soldered or brazed, respectively with which the metal tube cannot form a material bonded connection, respectively with which the metal tube can only with considerable technical effort form a fatigue resistant, material bonded connection. Particularly the above-mentioned internal rolling method, as well as also the above-mentioned external pressing method, have proven themselves as useful for the manufacture of measuring transducers of the vibration-type, especially also for affixing a metal tube useful as a measuring tube in a passageway of an end plate of a transducer housing, respectively of a metal body useful as support element. This not least of all also because both in the case of the internal rolling method, as well as also the press method, the particular force-based interlocking is introduced also by cold deformation of the measuring tube, respectively of the metal body, namely below a respective recrystallization temperature of the metal to be deformed, consequently each of the two methods is also performable at room temperature, respectively also without supply of heat. Moreover, by means of this method, sufficiently high holding forces, respectively holding forces exactly matched to the particular nominal diameters, can be achieved in very simple, equally as well effective, manner for producing a fatigue resistant connection between metal tube and metal body. Additionally, the so produced holding forces, consequently the therewith manufactured force-based interlocked connections, are not only highly loadable, but, instead, also reproducible within very narrow tolerance ranges, respectively tolerance ranges acceptable for high-quality, batch production. Moreover, neither in the case of the internal rolling nor in the case of the press method is the application of a pressurizing medium required, a pressurizing medium, in each case, to be filled into the metal tube to be processed, consequently a pressurizing medium causing increased technical effort.
A disadvantage of the above indicated methods known from the state of the art, respectively conventionally applied in the case of the manufacture of measuring transducers of the vibration-type, based on cold deformation of a metal body and/or a metal tube and serving for affixing the metal tube to the metal body, especially also the internal rolling method, as well as also the press method, is, however, to be found therein, that the wall of the respective metal tube, respectively the metal body, must for the purpose of establishing sufficiently high holding forces be deformed over a correspondingly large axially extending deformation region, namely a deformation region extending with a predeterminable length in the direction of an imaginary longitudinal axis of the metal tube. Since, on the one hand, the deformation region produces quite a mentionable contribution to the total length of the respective composite system, consequently to the installed length of a measuring transducer of the vibration-type formed therewith, while, on the other hand, measuring transducers of the vibration-type should typically have installed length to nominal diameter ratios of clearly less than 15:1, the length of the deformation region, which is obviously not usable for the actual oscillation measurement, is regularly so selected that it amounts to less than twice a caliber of the respective metal tube, while ideally corresponding only, for instance, to the caliber. Accordingly, an application of the actually very advantageous internal rolling method, as well as also the press method, is so far reserved for such composite systems, respectively therewith formed measuring transducers, in the case of which the particular metal tube has a wall thickness of greater than 1.5 mm as well as a caliber to wall thickness ratio, defined by a ratio of the caliber of the metal tube to its wall thickness, amounting to greater than 5, equally as well less than 30, ideally namely lying between 10 and 20.
Nevertheless, there is in increasing measure an interest also in having such measuring transducers of the vibration-type, consequently in such composite systems manufacturable by cold deformation, in the case of which the respective metal tubes useful as measuring tubes should have a wall thickness of less than 1.5 mm, respectively smaller than the respective caliber, consequently a caliber to wall thickness ratio of greater than 20, for example, for the purpose of improving measurement sensitivity and/or for the purpose of lessening a length of the respective measuring tube, in order, as a result, to be able to provide measuring transducers with shorter installed lengths, respectively also in the case of application of a sectionally bent measuring tube more compact measuring transducers than before.